Value of additional immunocytochemical stain for cytokeratin in the diagnosis of leptomeningeal involvement of metastatic carcinoma

Background: The purpose of this study was to describe potential pitfalls in the diagnosis of metastatic adenocarcinoma in cerebrospinal fluid (CSF) and to suggest additional work in association with cytokeratin immunocytochemistry for the proper diagnosis, especially in the specimens with low cellularity. Methods: We collected 267 cytologic specimens of CSF from patients, who were diagnosed over a 9-month period. Each of the individual samples were divided into half the sample size and processed via both, ThinPrep (TP) with Papanicolau stain and cytocentrifugation-based preparation (cytospin, CP) with immunocytochemical stain for cytokeratin. Results: Amongst the 267 cases, 45 cases from 22 patients were diagnosed to be positive for metastasis adenocarcinoma in CSF. TP with Papanicolau stain showed satisfactory cytomorphology when compared with specimen of CP preparation and cytokeratin immunocytochemical staining. All the TP processed cases belonged to satisfactory/superior categories based on the assessment of technical artifact, which potentially helps in decreasing diagnositc errors. However, in 10 out of 45 cases, diagnostic atypical cells were present only in one of the two slides. Conclusions: Immunocytochemical stain for cytokeratin along with TP processed specimen helps in decreasing potential diagnostic errors in the cytological diagnosis of metastatic carcinoma in CSF specimen.